A system composed of a thermochemical dipole using two reversible thermochemical phenomena is a known means for producing refrigeration. The thermochemical dipole comprises an LT reactor, an HT reactor and means for exchanging a gas between LT and HT. The two reactors are the site of reversible thermochemical phenomena chosen so that, at a given pressure in the dipole, the equilibrium temperature in LT is below the equilibrium temperature in HT.
The reversible phenomenon in the HT reactor involves a sorbent S and a gas G and may be:                a reversible adsorption of G by a microporous solid S;        a reversible chemical reaction between a reactive solid S and G; or        an absorption of G by a saline or binary solution S according to the scheme:“sorbent S”+“G”⇄“sorbent S+G”. The reversible phenomenon in the LT reactor involves the same gas G. It may be a liquid/gas phase change of the gas G or a reversible adsorption of G by a microporous solid S1, or a reversible chemical reaction between a reactive solid S1 and G, or an absorption of G by a solution S1, the sorbent S1 being different from S. The refrigeration production step of the device corresponds to the synthesis step in HT:“sorbent S”+“G”⇄“sorbent S+G”. The regeneration step corresponds to the decomposition step in HT:“sorbent S+G”→“sorbent S”+“G”. The production of refrigeration at a temperature Tf in a dipole (LT, HT) from a heat source at the temperature Tc and from a heat sink at the temperature To, implies that the thermochemical phenomenon in LT and the thermochemical phenomenon in HT are such that:        during the step of producing refrigeration by the dipole, the exothermic consumption of gas in HT takes place at a temperature close to and above To, which creates a pressure in the dipole such that the equilibrium temperature in the reactor LT is close to and below Tf; and        during the step of regenerating the dipole, the endothermic release of gas in HT is carried out at the temperature To, which creates a pressure in the dipole such that the temperature at which the exothermic consumption of gas in LT is carried out is close to and above To.        
The thermochemical phenomena currently used enable refrigeration to be produced at a negative temperature in LT, but they do not fulfill the above criteria with the objective of producing refrigeration at very low temperature (Tf typically from −20° C. to −40° C.) for long-lasting foodstuff preserving and freezing applications from a heat source, with the thermal potential of which is around 60 to 80° C., the heat sink generally composed of the ambient medium being at a temperature To of around 10° C. to 25° C. These phenomena either require, during the regeneration, a temperature Tc well above 70° C. to operate with a heat sink at the ambient temperature To, or they require a heat sink at a temperature below To if a heat source at Tc=60-80° C. is used.
For example, to produce refrigeration at −30° C. using a heat source at 70° C., when LT is the site of an L/G phase change of ammonia NH3, and HT is the site of a chemical sorption of NH3 by a reactive solid S: if S is BaCl2, a heat sink at 0° C. would be needed for the reactor LT during the refrigeration production step, whereas if S is CaCl2, a heat sink at −5° C., that is to say at a temperature well below To, would be needed during the regeneration step.
Solar energy or geothermal energy are advantageous heat sources, but they supply heat at a low temperature level which is not, in general, above 60-70° C. when a low-cost collection technology is used, such as for example flat collectors conventionally used for producing domestic hot water. The use of these types of energy consequently does not enable the intended aim to be achieved.